The present invention relates generally to polarization conversion systems for use in projection displays and, more particularly, to a polarization conversion system having an improved longevity, a reduced number of piece parts, lower fabrication costs and simplified component alignment.
Polarization conversion systems (PCS) are utilized in display projectors requiring polarized light for operation. The polarization conversion device (PCS) is positioned in the optical path after the illuminator and splits the light into two orthogonal polarization states rotating one to produce a combined beam of nearly uniform polarization.
There is in use today a compact PCS which utilizes a cemented array of rhombic glass prisms having prescribed beam splitting coatings for separating polarization states, mirror coatings to redirect the reflected split beam, and half-wave structures to rotate the reflected split beam. This is the typical function that a PCS is to perform.
The half-wave plates utilized in this structure are typically polymeric foils glued to the appropriate prism segments, and the glass prisms of the PCS are also assembled using an adhesive.
Because the adhesives commonly used in such existing PCS are affected by heat or radiation from the projection system illuminator, the performance of such a PCS has been found to degrade with service time. Such PCS units are fabricated of precisely ground and polished glass which is held together by adhesives which are found to degrade over a prolonged period of service time because of the exposure to the illuminator radiation. Therefore, while such PCS units are satisfactory in certain respects, they do tend to degrade with service time because of this exposure to heat or radiation from the system illuminator. Accordingly, the present invention is directed to overcoming one or more of the problems or disadvantages associated with the relevant technology.
In the preferred embodiment of this invention, the use of adhesives between the glass elements of the PCS is eliminated, and the polymer retarder foils and the adhesives used, if any, are immersed in a fluid which homogenizes the temperature at bright spots. Because the optical elements used with these PCS units are formed from pre-scribed glass sheets, which may be coated in large sections prior to being broken to the size specified, no grinding or polishing is required, nor is any treatment required of the edges. In this manner a polarization conversion system which is constructed in accordance with this invention will have improved longevity, a reduced number of parts which will simplify component alignment and will be less expensive to fabricate.